[Peter Raschendorfer]

After further digging into the code I’ve found the principal reason. It makes no difference if a member has created topics or not. The problem is the main query which always queries for posts. The 404 error appears if the user has not created any posts.

I’ve created a ticket: https://bbpress.trac.wordpress.org/ticket/3161

[Peter Raschendorfer]

Thanks for your response. The upcoming version 2.6 seems to solve the issue. I’ve tested it with 2.5.13 yet. Today I’ve tried 2.6-rc-3 and the 404 error is gone.

My testing environment is WP 4.8.1, no other plugins than bbPress, Twenty Seventeen Theme.

I’ve added the following lines to the Theme’s functions.php tp figure it out:

add_filter( '404_template', function() {
  global $wp_query;
  print_r( $wp_query );
  die();
} );

In bbPress 2.5.13 the 404_template filter fires and is_404 is true. In 2.6-rc-3 the filter does not fire.

Would you please do me favor and also check it with 2.5.13 just to be sure?

Thanks,
Peter